1. Field of Invention
The present invention relates to the use of ionic liquids as a medium for preparing sheets or films of a resin material containing Nanoparticles, wherein the Nanoparticles are highly oriented within the sheet or film.
2. Discussion of the Background
The production of nanomaterials requires energy intensive processes. Particular difficulty has been met when attempting to capture Nanoparticles and prevent their agglomeration, then align these Nanoparticles to produce an orderly array. This can often be attributed to the importance in the nanoscale world of Brownian motion and surface forces. These forces can be significant factors causing agglomeration, such as when strong surface forces make the moving parts of a NEMS device stick together and seize up. (Jones, Journal of Nanotechnology, August 2004).
A particularly desired oriented nanomaterial is a sheet or film made from a resin material, such as cellulose, in which aligned nanoscale magnetic particles are embedded. Such materials can be used as smart paper, and in magnetic information storage media. While it is well established that the storage capacity of recording media can be significantly increased by further reducing the grain size and distribution of magnetic particles in the thin film in order to increase the signal-to-noise ratio of the medium, upon reaching the nanoscale for the magnetic particles, it becomes increasingly difficult to adequately distribute the particles and avoid agglomeration. Further, it is necessary to increase the magnetic anisotropy of the resulting product in order to guarantee thermal stability of the recorded information.
Ionic liquids are now a well-established class of liquids containing solely ionized species, and having melting points largely below 150° C., or most preferably below 100° C. In most cases, ionic liquids (ILs) are organic salts containing one or more cations that are typically ammonium, imidazolium or pyridinium ions, although many other types are known.
Endres, Chem Phys Chem, 2002, 3, 144-154, discloses the electrodeposition of various materials, such as metals, onto substrates from ionic liquids.
Martin et al, Phys. Rev. E, 61(3), 2818-2830 (2000) disclose the production of magnetic field-structured composites (FSCs) by structuring magnetic particle suspensions in uniaxial or biaxial, e.g., rotating, magnetic fields, while polymerizing the suspending resin. However, since the suspensions are produced by polymerizing the resin in which the magnetic particles are suspended, the disclosed process can only be used with systems in which the suspending resin is prepared during the process.
When a magnetic particle suspension, containing multidomain particles, is exposed to a uniaxial magnetic field, the magnetic dipole moment on the particles will generally increase and align with the applied field. The particles will then migrate under the influence of the dipolar interactions with neighboring particles, to form complex chainlike structures. If a magnetic particle suspension is instead exposed to a biaxial (rotating) magnetic field, the induced dipole moments produce a net attractive interaction in the plane of the field, resulting in formation of a complex sheetlike structure. Similar effects occur when suspensions of dielectric particles are subjected to uniaxial or biaxial electric fields. These materials are known in the art as field-structured composites (FSCs). FSCs can have large anisotropies in properties such as conductivity, permittivity, dielectric breakdown strength, optical transmittance, etc. (Martin et al, ibid.)
There is thus a need for a method to reliably produce nanomaterials having aligned Nanoparticles contained in the material matrix, while also providing high magnetic anisotropy of the resulting material.